You need to manage the work of each developer with standard git branch/merge processes. When one dev is done with work in their feature branch, then they will create a pull request to merge changes into your collaboration branch.
If the second dev has not created a feature branch yet, they can just do so after the pull request from the first dev is complete and then continue work from there. If the second dev has already created a feature branch, then they will need to merge the new changes from the collaboration branch into their feature branch to continue work before later committing to git and creating a pull request to merge changes from their feature branch back into the collaboration branch. From there, you can publish as needed.
This git work can be done through the ADF editor as well as through any other git interface you have. It's up to you.
This article discusses the process in specific detail using the ADF editor.
EDIT:
I believe you now have answers for this from 3 of the other 5 questions you posted about this same topic in the past day.
ADF publish confusion in git mode
Azure data factory working-branch confusion
When ADF publish branch is git protected how to publish?
Here is another article which describes the fundamental git process for ADF to help bring you up to speed with the fundamentals of how the different branches work, and how you can switch publish branches on the fly if needed.
